Advances in optical storage media have been rapid, and in addition to such ROM (Read-Only Memory) media as CD-ROM and DVD-ROM, RAM (Random Access Memory) media such as CD-R, DVD-R, CD-RW, DVD-RW, and MO (Magneto-Optical) media have also come into use.
Such writeable optical storage media include dye type, phase-change type, and magneto-optical type media; in all cases, however, optical energy causes heating, to induce a dye change, phase change, or magneto-optical change, in order to record data. The optical energy (called the write power) to record data must be adjusted to an appropriate value according to the optical storage media.
With increases in data storage capacities in recent years, data storage densities have risen, and fine control of the LD power (write power) during writing has become vital. Normally when the power to a device is turned on and media which has been in the same environment is inserted, the temperatures of the device and media rise substantially equally, and so the write LD power can be controlled so as to be ideal.
However, when for example media which has been brought indoors from a cold outdoor environment is inserted into a device which has been in a heated room, the temperature of the media rises rapidly, and time is required until the temperature is the same as the device temperature; consequently there is a shift in the write LD power from the ideal power during this time.
FIG. 13 is a diagram of the change with time in the write power necessary when media at low temperature is inserted into a device at high temperature; the horizontal axis plots the time from media insertion (seconds), and the vertical axis plots the required write power (mW).
As shown in FIG. 13, when low-temperature media (approximately 25° C.) is inserted into a high-temperature device (for example, approximately 54° C.), the write power required at the time of media insertion is approximately 12.5 mW, but 600 seconds after insertion of the media, the required write power is approximately 10.5 mW.
Thus in methods in which the write power is adjusted through test writing at the time of media insertion, a shift in the write power occurs, and in the worst case write errors or time-out errors at the higher-level host due to extended retries occur, possibly causing data loss.
In order to resolve this problem, in the prior art a method has been proposed in which a temperature sensor has been provided to detect the temperature of the device, the media temperature is estimated from the optimum write power obtained from the results of a test write (trial writing) at the time of media insertion, and the write power is adjusted based on both detected temperatures and the elapsed time (see for example Japanese Patent Laid-open No. 4-076843 (FIG. 2 and FIG. 4)).
Further, in the prior art a method has been proposed in which a temperature sensor to detect the temperature of the device and another temperature sensor to detect the temperature of an inserted media cartridge are provided, and when the difference in the temperatures detected by the two temperature sensors is greater than a prescribed value, recording, reproduction, and erasure are inhibited (see for example Japanese Patent Laid-open No. 2-101675).
On the other hand, the earlier the timing for returning to normal processing from special processing in a state in which there is a temperature difference, the greater the effect. Both techniques described above entail judgment only of the temperature difference between device and media, so that when there are rapid fluctuations in the temperatures of the device and media, there is danger in returning to normal processing with early timing. Consequently in order to safely return to normal processing, the temperature difference for the return timing must be made small, and so early return to normal processing is difficult.
Further, in the former technique of the prior art, the write power adjusted value (absolute value) for test writing is scattered due to the states of the media and device, so that test writing must be performed a plurality of times, the average value computed, and the media temperature estimated. Consequently time is required for test writing, and the wait time until the media can be accessed is too long.
Moreover, in a MSR (Magnetic Super-Resolution) type optical disk, changes in characteristics occur due to shifts in sensitivity and for other reasons, and it is difficult to estimate the media temperature from write power adjusted values during test writing.
In the latter technique of the prior art, in addition to a device temperature sensor, a media temperature sensor is necessary, resulting in increased equipment costs. And, detection of the temperature of inserted media is difficult, and in order to perform accurate temperature detection a high-sensitivity sensor is required, further increasing costs. In the case of removable optical storage media in particular, the state of insertion is not constant, so that scattering arises in the temperature detected by the temperature sensor of the media.